The objectives of this proposal are to investigate the molecular characteristics of the opiate receptor with particular emphasis on the role of phospholipids and other lipids. Studies are aimed at elucidating the mechanism whereby phosphatidylserine (PS) enhances opiate binding; and preliminary evidence would suggest that the receptor is a protein complex maintained by PS in a conformation appropriate for binding. Another study is aimed at investigating the effect of modifying the physical state of the neural membranes and the role of calcium in opiate binding. Finally, attempts are underway to purify a Triton-solubilized extract of rat neural membranes which exhibits opiate binding. The solubilized receptor exhibits many of the same kinetic and chemical characteristics of the membrane-bound receptor.